Importing Brushes in 2.79 on Mac
Brushes are considered the same as any other part of Blender comparable to objects and materials - they are 'imported' through the Append function. If you have a brush(es) stored in a file, you press Append under File and then navigate to the file containing them. Select the ones you want, and confirm to append into your scene - then you should be able to find them in your current file. Check them to be Fake User if you want them to stay in the file after close and reopen.